Electric skateboard with strain-based controls and methods

ABSTRACT

An electric weight sensing skateboard using one or more strain gauge systems to detect rider-induced strain on one or both trucks, an inertial sensor to detect accelerations and balance position, and wheel speed sensors. Throttle is controlled by rider position, for example, lean forward to increase speed, lean back to slow down. Several drive methods include a rider position detection velocity setpoint control, torque setpoint control, and direct velocity/torque control. A throttle remote is not required. Rider weight activates the motors.

CROSS-REFERENCES

This application claims the benefit under 35 U.S.C. § 119(e) of thepriority of U.S. Provisional Patent Application Ser. No. 62/427,832(filed Nov. 30, 2016), the entirety of which is hereby incorporated byreference for all purposes.

INTRODUCTION

The popularity of electric skateboards has grown considerably over thepast several years. Many companies have entered this market, withslightly differing designs. Generally speaking, these vehicles require ahandheld remote, lack the ability to sense the rider's body position tocontrol the throttle and detect the rider, and have suffered fromvarious issues, such as safety and reliability problems related torequiring the rider to manually control the throttle with a handheldremote, and a lack of rider-on detection, and a lack of ability toreduce drivetrain drag when the rider is manually pushing. A need existsfor a more intuitive, reliable, safer control system for these electricvehicles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric front oblique view of an illustrativefour-wheeled weight-sensing electric skateboard having induced-strainrider detection and induced-strain throttle controls in accordance withaspects of the present disclosure.

FIG. 2 is a bottom view of the vehicle of FIG. 1.

FIG. 3 is a close up view of the rear truck with strain gauge and dualmotors of the vehicle of FIG. 1.

FIG. 4 is a close up view of the front truck with strain gauge of thevehicle of FIG. 1.

FIG. 5 is a schematic circuit diagram of an illustrative strain gaugesensor and amplification circuit suitable for use in vehicles describedherein.

FIG. 6 is a plan view of an illustrative full bridge strain gauge sensorsuitable for use in vehicles described herein.

FIG. 7 is a isometric view of a spring steel suspension truck withstrain gauge mounted suitable for use in vehicles described herein

FIG. 8 is a side view of FIG. 7

FIG. 9 is a flow chart depicting steps in an illustrative method forrider detection in accordance with aspects of the present disclosure.

FIG. 10 is a flow chart depicting steps in an illustrative method forcontrolling vehicle throttle with a DUAL STRAIN GAUGE SPEED CONTROLLER

FIG. 11 is a flow chart depicting steps in an illustrative method forcontrolling vehicle throttle with a DUAL STRAIN GAUGE TORQUE CONTROLLER

FIG. 12 is a flow chart depicting steps in an illustrative method forcontrolling vehicle throttle with a DUAL STRAIN GAUGE DIRECT TORQUECONTROLLER

FIG. 13 is a flow chart depicting steps in an illustrative method forcontrolling vehicle throttle with a SINGLE STRAIN GAUGE SPEED CONTROLLER

FIG. 14 is a flow chart depicting steps in an illustrative method forcontrolling vehicle throttle with a SINGLE STRAIN GAUGE TORQUECONTROLLER

FIG. 15 is a flow chart depicting steps in an illustrative method forcontrolling vehicle throttle with a SINGLE STRAIN GAUGE DIRECT TORQUECONTROLLER

FIG. 16 is a flow chart depicting steps in an illustrative method forcontrolling vehicle throttle with a DUAL STRAIN GAUGE DIRECT VELOCITYCONTROLLER

FIG. 17 is a flow chart depicting steps in an illustrative method forcontrolling vehicle throttle with a SINGLE STRAIN GAUGE DIRECT VELOCITYCONTROLLER

FIG. 18 is a block diagram depicting selected components in anillustrative control system in accordance with aspects of the presentdisclosure.

DESCRIPTION

Various aspects and examples of an electric skateboard havingstrain-based controls, as well as related methods, are described belowand illustrated in the associated drawings. Unless otherwise specified,an electric skateboard in accordance with the present teachings, and/orits various components, may, but are not required to, contain at leastone of the structure, components, functionality, and/or variationsdescribed, illustrated, and/or incorporated herein. Furthermore, unlessspecifically excluded, the process steps, structures, components,functionalities, and/or variations described, illustrated, and/orincorporated herein in connection with the present teachings may beincluded in other similar devices and methods, including beinginterchangeable between disclosed embodiments. The following descriptionof various examples is merely illustrative in nature and is in no wayintended to limit the disclosure, its application, or uses.Additionally, the advantages provided by the examples and embodimentsdescribed below are illustrative in nature and not all examples andembodiments provide the same advantages or the same degree ofadvantages.

Examples, Components, and Alternatives

The following sections describe selected aspects of exemplary electricskateboards, as well as related systems and/or methods. The examples inthese sections are intended for illustration and should not beinterpreted as limiting the entire scope of the present disclosure. Eachsection may include one or more distinct embodiments or examples, and/orcontextual or related information, function, and/or structure.

Definitions

The following definitions apply herein, unless otherwise indicated.

“Substantially” means to be essentially conforming to the particulardimension, range, shape, concept, or other aspect modified by the term,such that a feature or component need not conform exactly. For example,a “substantially cylindrical” object means that the object resembles acylinder, but may have one or more deviations from a true cylinder.

“Comprising,” “including,” and “having” (and conjugations thereof) areused interchangeably to mean including but not necessarily limited to,and are open-ended terms not intended to exclude additional, unrecitedelements or method steps.

Terms such as “first”, “second”, and “third” are used to distinguish oridentify various members of a group, or the like, and are not intendedto show serial or numerical limitation.

Electric Weight Sensing Skateboard:

Electric skateboards according to the present teachings overcome theissues described above by using one or more strain gauge systems todetect rider-induced strain on one or both trucks (wheel/axleassemblies), an inertial sensor to detect accelerations and balanceposition, and wheel speed sensors.

The present disclosure provides systems, apparatuses, and methodsrelating to electric skateboards. In some embodiments, electricskateboards may include:

A skateboard (FIG. 1-4) including a deck 101 to receive the feet of arider; one (or multiple) motors 102 (bldc hub motors or external beltdriven motors) and motor controller 103 and battery 105 and wheels 104disposed on front skateboard truck 106 and rear skateboard truck 108configured to propel the electric skateboard 100; a first strain gauge110 attached to a skateboard truck and configured to sense rider weightand center of gravity strain on the skateboard 100 induced by imbalancedforces exerted upon the front truck 106 and rear truck 108; an optionalsecond strain gauge 112 attached to the other truck and configured tosense rider weight and center of gravity strain on rear truck 108 andthe deck 101 induced by forces exerted upon the front and rear trucks106,108; at least one drive motor 102 configured to drive at least onewheel 104, wherein the drive motor(s) 102 are configured to drive thewheels 104 in response to weight imbalance of the deck 101 and ridercenter of gravity sensed by the strain gauge(s) 110,112, to cause thevehicle 100 to move linearly in response to forces on the front and reartrucks 106,108 and are only (or variably) activated (FIG. 9) by straingauge 110,112 sensing of the rider's weight as to not activate whenthere is no rider on the skateboard deck 101 and only when the inertialsensors 114 determine a substantially level vehicle 100.

An inertial balance sensor 114 attached to the deck 101 and configuredto sense inclination of the board 100, wherein the drive motor(s) 102are configured to drive the wheels 104 only when the skateboard 100 isproperly oriented in a reasonable riding position, such as substantiallylevel to the ground.

If only a single strain gauge 110 is utilized, a method will be used toallow the rider to zero the strain gauge 110 signal while standingcentered on the board deck 101, this tared zero setpoint will be used todetermine the difference in the strain gauge 110 measurement from zeroand therefore the center of gravity position of the rider.

Many different motor drive methods (FIG. 10-17) may be selected by therider through means such as a smartphone with a wireless connection.

One such method (FIG. 10,13) is to control the velocity setpoint of theskateboard and rider determined by using the strain gauge(s) to sensethe center of gravity (CG) of the rider; wherein, when the CG is sensedtoward the forward truck the desired speed will be incremented faster inthe speed controller loop; and when the CG is sensed toward the reartruck the desired speed will be decremented slower in the speedcontroller loop; the rate of increment/decrement may be determined bythe amplitude of the CG from center. This method has the advantage ofallowing the rider to comfortably stand centered on the board whilepowering forward at the desired speed. The rider would lean forward toaccelerate (increase velocity), lean back to slow down (decreasevelocity) until zero speed is reached.

Another control method (FIG. 11, 14) is to use the above describedmethod to sense CG but to increment or decrement a torque set point in atorque controller loop instead of a speed controller loop. The riderwould lean forward to increment the commanded torque set point and leanback to decrement the commanded torque set point; the rate ofincrement/decrement may be determined by the amplitude of the CG fromcenter.

A selectable option would allow advanced riders to, when leaning back,also continue in reverse after zero speed is reached.

Another control method (FIG. 12, 15) is to use the sensed CG to directlycontrol the commanded motor drive torque setpoint. The rider would needto continually lean forward to maintain forward torque and maintain alean back to apply negative torque.

Another control method (FIG. 16, 17) is to use the sensed CG to directlycontrol the commanded motor drive velocity setpoint. The rider wouldneed to continually lean forward to maintain forward velocity and leanback to reduce velocity.

A manual coasting mode may be selected wherein an inertial sensorattached to the board and configured to sense accelerations from riderpumps (pushes) and inclination of the board, the drive motor(s) beingconfigured to command a motor torque to cause the vehicle to have verylittle or no drag feeling in the drive train when a rider push is sensedby the inertial sensor or strain gauge(s). The controller in manual modewill be self-powered by regenerated power from the drive motors, theminimal amount of regeneration power is captured to run the controllerand allow the low-drag torque control as this mode is useful when thebattery has been nearly depleted.

A traction sensing controller is configured to sense the wheel speedsand adjust drive motor torque to keep the wheel rotational velocitiesrelatively similar, especially in situations when one drive wheel hasmore traction compared to the other which may be sensed by a controllerconfigured to read the strain gauge sensors on the trucks and determinewhich wheel has more rider weight and therefore more traction.

Springed suspensions 200 (FIG. 7,8) on the trucks 106,108 between thewheels and deck are utilized to improve ride comfort, traction, stuckwheels, and reduce rider fatigue. Strain gauges 110,112 may be mounteddirectly to the spring suspensions 200 to measure the induced stresscaused by the rider's weight.

A folding deck configured to hinge near the middle with one trucknesting in front or behind the other truck improves portability.

Features, functions, and advantages may be achieved independently invarious embodiments of the present disclosure, or may be combined in yetother embodiments, further details of which can be seen with referenceto the following description and drawings.

The rider weight measurement may also be used to set the aggressivenessof the proportional-integral-derivative (PID) speed/torque controller(also referred to as a PID loop) of the motor controller. For example, asofter control may automatically be implemented for lightweight riders,and a stronger, more aggressive control for heavier riders, therebygreatly adding to the safety of the vehicle.

FIG. 6 is a plan view of an illustrative full bridge strain gauge sensorsuitable for use in vehicle 100 and others. FIG. 5 is a schematiccircuit diagram of an illustrative strain gauge sensor and amplificationcircuit suitable for use in vehicle 100 and others.

The drive arrangement may use any combination of brushless directcurrent (i.e., BLDC) hub motors 102 with integrated tires 104. In otherexamples, a separate wheel and drive motor (brushed or brushless) may beutilized, with power transferred via a chain or belt or transmission. Insome examples, a hubless wheel may be driven by a friction drive motor.

An inertial balance position sensor 114 is coupled (e.g., mounted) todeck 101, and configured to sense a tilt position of the vehicle.Balance position sensor 114 may include a combinedmicroelectromechanical systems (MEMS) inertial sensor, such as asix-axis rate gyro and accelerometer. In some examples, sensor 114 isconfigured to provide a measurement of the position (inclination andinertial movement) of the entire vehicle 100. Sensor 114 is preferablymounted on a circuit board 103 which is attached to deck 101. Sensor 114may be disposed in any suitable location on the frame. However, alocation closer to the center of the vehicle may provide reducedcentrifugal force errors caused by vehicle movement.

A rechargeable battery 105 and battery protection circuit is mounted todeck 101 to provide power for the vehicle. Battery 105 may include anysuitable power storage device, such as a lithium ion battery.

A first full-bridge strain gauge 110,112 is bonded onto a truck 106,108of skateboard 100. An example of a full-bridge strain gauge is shown inFIG. 6. Strain gauge 110,112 may include a flexible, insulatingsubstrate 138 supporting one or more conductive foil zig-zag patterns140. Deformation of pattern 140 changes the electrical resistance of thepattern, which can be measured at leads 141. The change in resistancecan then be used to infer the magnitude of induced stress, according toknown methods.

Strain gauge 110,112 may be located at or near center region of truck106,108, or anywhere a majority of strain is induced onto the truckcaused by the rider's weight. In some examples, a single or half-bridgestrain gauge may instead be used. In this example, strain gauge 110,112is bonded to truck 106,108 longitudinal with the axle on a bottomsurface, such that the strain gauge will detect strains from the rider'sweight.

As shown in FIG. 5, the analog output of strain gauge 136 may beamplified with an amplifier circuit 142. Circuit 142 may include anysuitable amplification components, and is illustrative in nature. Therider's weight on a truck can be derived from the analog voltage, whenan operational amplifier is used to detect the voltage shift caused bythe strain gauge pairs stretching and/or compressing in response to theinduced stresses on the truck. Circuit 142 provides a method formeasuring these small voltage changes and supplying an output voltage(corresponding to the rider's weight) to a microcontroller (see FIG.18). As the rider steps anywhere onto the skateboard deck, a strain isinduced and detected by the strain gauge sensor 110,112, therebyindicating when a rider is present and enabling the motor drive system.A magnitude of the induced stress may be proportional to rider weight.This control system may be referred to as the rider-detect system orrider detection. When the rider steps off the vehicle the control systemwill stop driving the wheels (e.g., by shutting off the motors), suchthat the vehicle comes to a stop, and/or may disable the motor(s).

The rider's weight may be precisely calculated based on a magnitude ofthe detected strain, and this weight may be used to adjust theaggressiveness of the throttle control and motor current PID loop. Thisfacilitates a less aggressive control with a lightweight rider and atighter more aggressive control for a heavier rider, with granularvariation in between. This feature increases safety and helps to preventfalls from an overly aggressive system with light rider, or from anunderpowered system with heavy rider. In other words, the vehicle'sthrottle loop will be matched appropriately to the rider's weight, assensed by the strain gauge(s).

In examples where rider modes are selectable, for example, a new ridermay select a more sluggish, less responsive “learning” mode thatprovides a safer and more comfortable system. Meanwhile, an expert ridermay select a very fast and responsive system. In some examples, thisrider mode can be communicated to motor controller circuit 103 through awireless connection device 150 disposed on vehicle 100, such as aBluetooth Smart (also known as BLE) module, e.g., using a smartphoneapp.

In some examples, vehicle 100 may save in memory the desired settings ofeach individual rider, e.g., according to his or her measured weight,and/or may recall a previously established profile (e.g., through awireless connection to a smartphone). Such a profile may includeinformation regarding throttle aggressiveness, maximum speed, and/or thelike.

Strain gauges are initially calibrated to center when zero strain isapplied to the frame. However, strain gauges have a known tendency fortheir accuracy to drift over time. In some examples, the control logicof vehicle 100 may calibrate, upon startup, the zero points of any orall strain gauges. The calibration may be averaged and saved in memoryover several startup events to prevent inadvertent strain adverselyaffecting the calibration. Accordingly, as the vehicle is used it willbe gradually calibrated with each power-on cycle.

The user may be directed to power the vehicle without any weight orstrain applied to the frame, such that at startup the strain gauges canbe automatically zeroed/centered to cancel out drift. Drift will begradual over time, so this power-up calibration may be configured toaffect the drift value by a small amount, as to avoid erroneouscalibration by an accidental strain applied during startup.

An erroneous calibration may be detected for example if, upon power-up,a very large calibration need is measured. This error will be ignoredand the rider may be warned accordingly. A full user-initiatedcalibration method may be provided as well (e.g., a “tare” button orcommand).

In some examples, strain gauges may be centered by detecting when asensor is being quickly saturated while vehicle 100 is ridden. In theseexamples, the gauge will be slowly centered over time to ensure fullmovement in both directions. In some examples, center calibration of thezero point of a strain gauge may be achieved using a digital to analogconverter (DAC) output of the microcontroller connected to the straingauge through a high value resistor (e.g., 470K Ohms). This DAC outputwill essentially replace a potentiometer 152 of circuit 142, 146 (seeFIG. 5) and allow the microcontroller to adjust the center points of thestrain gauge full bridge system.

In some examples, a remote control feature may be implemented to controlvehicle 100 using a portable electronic device (e.g., a smartphone) andinstalled app or handheld remote, via wireless module 150. This featuremay be enabled or disabled by the rider detection circuit, the riderdetection weight threshold may be adjusted using the rider's smartphoneapp and wireless module 150, such that only riders above a certainweight are permitted to use the vehicle (e.g., preventing children fromunauthorized use).

Vehicle 100 may further include instructions 414 stored in a memory 416of a data processing system 418 (e.g., a personal computer) having itsown processor 420. Instructions 414 may be supplied to computer 418 as adownload from a computer network (e.g., the Internet) or on a physicalmedium (e.g., on a portable memory storage device such as a thumb drive,CD, or DVD). Control system 400 may be configured to connect to computer418, which may upload instructions 414 to vehicle 100. Instructions 414and computer 418 may provide for modification of instructions orparameters stored in memory 408 of the balance control system. Controlsystem 400 may connect to computer 418 through wired or wirelessmethods, e.g., by a data cable or by a wireless connection using radiofrequency signals and protocols, or by other suitable wireless means.

CONCLUSION

The disclosure set forth above may encompass multiple distinct exampleswith independent utility. Although each of these has been disclosed inits preferred form(s), the specific embodiments thereof as disclosed andillustrated herein are not to be considered in a limiting sense, becausenumerous variations are possible. To the extent that section headingsare used within this disclosure, such headings are for organizationalpurposes only. The subject matter of the invention(s) includes all noveland nonobvious combinations and subcombinations of the various elements,features, functions, and/or properties disclosed herein. The followingclaims particularly point out certain combinations and subcombinationsregarded as novel and nonobvious. Other combinations and subcombinationsof features, functions, elements, and/or properties may be claimed inapplications claiming priority from this or a related application. Suchclaims, whether broader, narrower, equal, or different in scope to theoriginal claims, also are regarded as included within the subject matterof the present disclosure.

What is claimed is:
 1. An electric skateboard, comprising: a platformfor a rider; ground contacting wheels; a first strain gauge attached tothe skateboard and configured to sense induced strain by imbalancedforces exerted upon the platform; a first drive motor configured todrive a ground contacting wheel in response to sensed induced strain. 2.The vehicle of claim 1, further comprising a second strain gaugeattached to the skateboard and configured to sense strain in theplatform induced by a rider's weight exerted upon the platform.
 3. Thevehicle of claim 1, wherein the drive motor is configured to driveground contacting wheels with a speed controller responding to a speedsetpoint incremented or decremented by the rider position.
 4. Thevehicle of claim 1, wherein the drive motor is configured to driveground contacting wheels with a torque controller responding to a torquesetpoint incremented or decremented by the rider position.
 5. Thevehicle of claim 1, wherein the drive motor is configured to driveground contacting wheels with a torque controller responding to a torquedetermined by the rider position.
 6. The vehicle of claim 1, wherein thedrive motor is configured to drive ground contacting wheels with avelocity controller responding to a velocity determined by the riderposition.
 7. The vehicle of claim 1, wherein a balance position sensorenables drive motor.
 8. The vehicle of claim 1, wherein a strain gaugeinduced stress threshold enables drive motor.
 9. The vehicle of claim 1,wherein the vehicle is self powered by regenerated motor power toactivate a near zero torque motor control.
 10. The vehicle of claim 1,wherein the vehicle has a sprung suspension between the groundcontacting wheels and the platform.
 11. An electric skateboard,comprising: a deck for a rider; ground contacting wheels; a drive motorconfigured to drive a ground contacting wheel; a strain gauge attachedto the skateboard and configured to sense induced strain exerted uponthe deck; a speed controller, with a speed setpoint which is configuredto increment and decrement in response to the sensed induced strain. 12.An electric skateboard, comprising: a platform for a rider; groundcontacting wheels; battery; a drive motor configured to drive a groundcontacting wheel; a first strain gauge attached to the skateboard andconfigured to sense first induced strain exerted upon the front of theplatform; a second strain gauge attached to the skateboard andconfigured to sense second induced strain exerted upon the rear of theplatform; a controller configured to determine the rider's center ofgravity according to the first induced strain and the second inducedstrain; a motor speed controller, with a speed setpoint which isconfigured to increment and decrement in response to the rider's centerof gravity.
 13. The vehicle of claim 12, wherein the sum of the firstinduced strain and the second induced strain enables the drive motor.